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CVE-2026-97206 (GCVE-0-2026-97206)
Vulnerability from cvelistv5 – Published: 2026-10-21 08:57 – Updated: 2026-10-21 08:57
VLAI
EPSS
VEX
Title
DNS-over-QUIC (DoQ) path-migration can lead to use-after-free on multi-threaded deployments.
Summary
NLnet Labs Unbound, 1.22.0 up to and including version 1.26.1, contains a DNS-over-QUIC (DoQ) lifetime bug reachable by a remote DoQ client under multi-threaded operation. A client-triggered QUIC path migration can enter stream/connection cleanup while a mesh reply still retains a pointer to the DoQ stream. Cleanup frees the DoQ stream and when the pending mesh reply later completes it dereferences a stale pointer leading to a crash.
Severity
7.5 (High)
CWE
- CWE-416 - Use After Free
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | Unbound |
Affected:
1.22.0 , < 1.26.2
(semver)
|
Date Public
2026-10-21 00:00
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CVE-2026-96405 (GCVE-0-2026-96405)
Vulnerability from cvelistv5 – Published: 2026-10-21 08:57 – Updated: 2026-10-21 08:57
VLAI
EPSS
VEX
Title
Aggregate DNS name chained pointer decompression work leads to degradation of service.
Summary
NLnet Labs Unbound up to and including version 1.26.1 limits compression-pointer traversal for each individual domain-name operation but has no aggregate inbound decompression-work budget. Many chained compression pointers in a message results in a lot of CPU usage following them. A malicious actor with recursive-query access and control of an ordinarily delegated authority that serves specially crafted replies can exploit the vulnerability and degrade Unbound's general performance.
Severity
5.3 (Medium)
CWE
- CWE-770 - Allocation of Resources Without Limits or Throttling
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | Unbound |
Affected:
0 , < 1.26.2
(semver)
|
Date Public
2026-10-21 00:00
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CVE-2026-50106 (GCVE-0-2026-50106)
Vulnerability from cvelistv5 – Published: 2026-10-21 08:57 – Updated: 2026-10-21 08:57
VLAI
EPSS
VEX
Title
Possible insecure NXDOMAIN for non-existing records under a configured island trust anchor underneath an insecure parent.
Summary
When NLnet Labs Unbound up to and including version 1.26.1 is configured with both a root trust anchor and an additional 'trust-anchor:' for an island-of-security zone whose parent is provably insecure under the root chain, a malicious actor who can deliver one forged NXDOMAIN response for a name inside the island, with the NSEC/SOA RRSIG 'SignerName' set to the insecure parent, tricks Unbound's validator to use the root trust anchor instead, and consecutively the insecure parent, thus causing that record to be treated as insecure and denying existence for records in the trust island.
Severity
6.5 (Medium)
CWE
- CWE-807 - Reliance on Untrusted Inputs in a Security Decision
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | Unbound |
Affected:
0 , < 1.26.2
(semver)
|
Date Public
2026-10-21 00:00
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CVE-2026-35501 (GCVE-0-2026-35501)
Vulnerability from cvelistv5 – Published: 2026-10-21 08:56 – Updated: 2026-10-21 08:56
VLAI
EPSS
VEX
Title
Bypass of a configured island trust anchor underneath an insecure parent from an atacker-controlled NSEC record.
Summary
When NLnet Labs Unbound 1.0.1 up to and including version 1.26.1 is configured with both a root trust anchor and an additional 'trust-anchor:' for an island-of-security zone whose parent is provably insecure under the root chain, a malicious actor with a forged NSEC reply with the SOA bit cleared can trick Unbound to treat the configured trust island as insecure. This happens because the DNSSEC validator in Unbound accepts and caches the NSEC insecure response bypassing the RRSIG validation that the validator was supposed to do. The acceptance of the NSEC record at the trust anchor apex was allowed due to and old fix for type DS and NSEC queries from clients when trust anchor for that name existed.
Severity
CWE
- CWE-354 - Improper Validation of Integrity Check Value
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | Unbound |
Affected:
1.0.1 , < 1.26.2
(semver)
|
Date Public
2026-10-21 00:00
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CVE-2026-109125 (GCVE-0-2026-109125)
Vulnerability from cvelistv5 – Published: 2026-10-21 08:56 – Updated: 2026-10-21 08:56
VLAI
EPSS
VEX
Title
Possible cache poisoning vulnerability via a cache side-channel exposed by 'unwanted-reply-threshold'
Summary
In NLnet Labs Unbound up to and including version 1.26.1, an observable cache-level side-channel can be exposed with 'unwanted-reply-threshold > 0' configurations (not a default configuration). If a response-like UDP datagram reaches the upstream source port currently used by a recursive query, but its TXID does not match any pending query, Unbound counts the packet as an unwanted reply. When the accumulated count reaches the configured threshold, Unbound clears the worker's RRset cache and message cache. This cache clear action does not destroy the current upstream UDP pending query. Therefore, an external observer can distinguish whether a candidate port matches the current upstream source port by checking whether an existing cached item has been cleared. This is a cache side-channel vulnerability that can be used to probe the upstream source port. Although the attack is not feasible on default configurations and the suggested value (10 million) makes it an ureliable attack on a public resolver, in scenarios where the attacker can keep a concurrent query window alive, the attacker can first filter the source port and then perform birthday-style guessing against the TXID, making cache poisoning a feasible attack path.
Severity
5.3 (Medium)
CWE
- CWE-205 - Observable Behavioral Discrepancy
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | Unbound |
Affected:
0 , < 1.26.2
(semver)
|
Date Public
2026-10-21 00:00
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CVE-2026-101341 (GCVE-0-2026-101341)
Vulnerability from cvelistv5 – Published: 2026-10-14 10:56 – Updated: 2026-10-14 14:08
VLAI
EPSS
VEX
Title
Stack overwrite from specially formatted TXT-DATA RDATA field
Summary
Tokens of text in RDATA (of for example TXT records) under 32 bytes are not checked to stay within the space reserved for the RDATA allowing for arbitrary sized out of bound stack writes, including an overwrite of a callback function pointer which is called directly after parse. Zone files which are written out by NSD itself, such for zones for which the NSD instance is secondary, will not be formatted like this. The zone file must be fed to NSD directly, (but it could come, for example, from an operator controlled provisioning system).
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-14 14:08 UTC
CWE
- CWE-121 - Stack-based Buffer Overflow
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-1… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | NSD |
Affected:
4.10.0 , < 4.15.3
(semver)
|
Date Public
2026-10-14 12:00
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CVE-2026-101339 (GCVE-0-2026-101339)
Vulnerability from cvelistv5 – Published: 2026-10-14 10:56 – Updated: 2026-10-14 14:08
VLAI
EPSS
VEX
Title
Stack overwrite from a specially crafted and formatted HIP RR
Summary
A HIP resource record that fills the RDATA near or at is limit, and has another dname RDATA field (a HIP Rendezvous server) can overwrite the stack with up to 191 bytes of attacker controlled data. Zone files which are written out by NSD itself, such as for zones for which the NSD instance is secondary, will not be formatted like this. The zone file must be fed to NSD directly, (but it could come, for example, from an operator controlled provisioning system).
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-14 14:08 UTC
CWE
- CWE-121 - Stack-based Buffer Overflow
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-1… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
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Affected:
4.10.0 , < 4.15.3
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|
Date Public
2026-10-14 12:00
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CVE-2026-101338 (GCVE-0-2026-101338)
Vulnerability from cvelistv5 – Published: 2026-10-14 10:56 – Updated: 2026-10-14 14:09
VLAI
EPSS
VEX
Title
Stack overwrite from a specially crafted and formatted SVCB or HTTPS RR
Summary
When a SVCB or HTTPS RR has filled the wire format RDATA up to the brim, another ECH parameter may overwrite the stack, and once beyond the limit, the base64 decoder can write attacker controlled data of unlimited size. Zone files which are written out by NSD itself, such as for zones for which the NSD instance is secondary, will not be formatted like this. The zone file must be fed to NSD directly, (but it could come, for example, from an operator controlled provisioning system).
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-14 14:09 UTC
CWE
- CWE-121 - Stack-based Buffer Overflow
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-1… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | NSD |
Affected:
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|
Date Public
2026-10-14 12:00
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CVE-2026-101337 (GCVE-0-2026-101337)
Vulnerability from cvelistv5 – Published: 2026-10-14 10:56 – Updated: 2026-10-14 14:09
VLAI
EPSS
VEX
Title
Stack overwrite from specially formatted base64 RDATA field
Summary
When base64 data is split up in pieces, of 3 character or less, tokens were incorrectly calculated to produce 0 bytes. This enables attackers to overwrite the stack with up to 64K of attacker controlled data. Zone files which are written out by NSD itself, such as for zones for which the NSD instance is secondary, will not be formatted like this. The zone file must be fed to NSD directly, (but it could come, for example, from an operator controlled provisioning system).
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-14 14:09 UTC
CWE
- CWE-121 - Stack-based Buffer Overflow
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-1… | vendor-advisory |
Impacted products
1 product
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|---|---|---|---|
| NLnet Labs | NSD |
Affected:
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(semver)
|
Date Public
2026-10-14 12:00
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CVE-2026-85501 (GCVE-0-2026-85501)
Vulnerability from cvelistv5 – Published: 2026-09-16 08:32 – Updated: 2026-09-16 14:12
VLAI
EPSS
VEX
Title
Retrap: Novel Vulnerabilities to launch Algorithmic Complexity Attacks on DNSSEC
Summary
Novel vulnerabilities to launch algorithmic complexity attacks on DNSSEC have been researched under the term 'ReTrap'. These result in degradation of service when malicious zones are used to serve the algorithmic complexity vulnerabilities. NLnet Labs Unbound up to and including 1.26.0 is vulnerable to some of them. TagTrap, where the triple(Zone, Algo, KeyTag) matching mechanism introduces a significant attack vector when resolvers handle malicious responses containing numerous mismatched DNSKEY, RRSIG, and DS record. DelegationTrap, where constructing the chain-of-trust requires iterative validation of DNSKEY and DS records from the root zone downward. For deeply nested domains, this results in significant computational overhead. NsecTrap, where responses with excessive invalid NSEC records compel the resolver to validate each one. AdditionalTrap, where Unbound by default would try to DNSSEC validate the ADDITIONAL section as well. This can be exploited to waste validation resources by malicious users.
Severity
5.3 (Medium)
SSVC
Exploitation: none
Automatable: yes
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-16 14:10 UTC
CWE
- CWE-770 - Allocation of Resources Without Limits or Throttling
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | Unbound |
Affected:
0 , < 1.26.1
(semver)
|
Date Public
2026-09-16 00:00
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CVE-2026-82720 (GCVE-0-2026-82720)
Vulnerability from cvelistv5 – Published: 2026-09-16 08:32 – Updated: 2026-09-16 14:14
VLAI
EPSS
VEX
Title
Use-after-free in DoH stream cleanup code path
Summary
NLnet Labs Unbound 1.12.0 up to and including 1.26.0 has a use-after-free vulnerability when compiled for DNS-over-HTTPs support with '--with-libnghttp2'. During failure code paths (i.e., RPZ drop query, jostle due to heavy traffic), a dropped DoH stream brings down the whole DoH session and does not account properly for other DoH streams in the same session. This leads to use-after-free in those code paths. If the prerequisites are satisfied (possible RPZ drop or heavy client traffic), a malicious actor can trigger the vulnerability with a single DoH connection and the appropriate traffic. Impact is limited as the reads are not user controlled and the use-after-free leads to early returns. However, a hardened allocator can catch the use-after-free and controllably terminate the process resulting to denial of service.
Severity
5.9 (Medium)
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-16 14:13 UTC
CWE
- CWE-416 - Use After Free
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | Unbound |
Affected:
1.12.0 , < 1.26.1
(semver)
|
Date Public
2026-09-16 00:00
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CVE-2026-82717 (GCVE-0-2026-82717)
Vulnerability from cvelistv5 – Published: 2026-09-16 08:31 – Updated: 2026-09-16 14:15
VLAI
EPSS
VEX
Title
CNAME synthesis could lead to heap corruption
Summary
In NLnet Labs Unbound up to and including 1.26.0, a vulnerability was found in that can progressively corrupt heap memory and under certain systems and compilation options could lead to remote code execution. The vulnerability starts when CNAME synthesis during an upstream response needs to enforce(rewrite) a max TTL value in the packet buffer. Coupled with a compression pointer that points to the overwritten value and invalidates the domain name, it leads to an error path that does not properly move the buffer position and allows for the heap buffer overflow. Since this is heavily reliant on heap memory layout, results are memory corruption that eventually leads to a crash and under specific systems and compilation options remote code execution.
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-16 14:15 UTC
CWE
- CWE-122 - Heap-based Buffer Overflow
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | Unbound |
Affected:
0 , < 1.26.1
(semver)
|
Date Public
2026-09-16 00:00
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CVE-2026-81642 (GCVE-0-2026-81642)
Vulnerability from cvelistv5 – Published: 2026-09-16 08:30 – Updated: 2026-09-16 14:32
VLAI
EPSS
VEX
Title
Heap buffer overflow and possible Remote Code Execution when digesting DNSKEY
Summary
In NLnet Labs Unbound up to and including 1.26.0, a vulnerability was found in the DNSSEC validator that enables denial of service and possible remote code execution as a result of digesting DNSKEYs. A DNSKEY with an owner compression pointer to its own RDATA can overflow the digest buffer. Remote code execution is possible through attacker controlled data. An adversary can exploit the vulnerability by controlling a malicious zone and querying a vulnerable Unbound.
Severity
SSVC
Exploitation: none
Automatable: yes
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-16 14:30 UTC
CWE
- CWE-122 - Heap-based Buffer Overflow
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | Unbound |
Affected:
0 , < 1.26.1
(semver)
|
Date Public
2026-09-16 00:00
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CVE-2026-81634 (GCVE-0-2026-81634)
Vulnerability from cvelistv5 – Published: 2026-09-16 08:30 – Updated: 2026-09-16 14:32
VLAI
EPSS
VEX
Title
Possible heap buffer overflow during DNSSEC canonicalization
Summary
In NLnet Labs Unbound up to and including 1.26.0, a 255 length query name with a large TCP response can lead to a heap buffer overflow during the RRSet canonicalisation routine. This is caused by missing to add the first owner name into the buffer length check. A malicious actor operating a malicious name server or tampering with an incoming response to Unbound (canonicalisation happens before DNSSEC validation), can trigger the vulnerability.
Severity
7.5 (High)
SSVC
Exploitation: none
Automatable: yes
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-16 14:32 UTC
CWE
- CWE-122 - Heap-based Buffer Overflow
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
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| NLnet Labs | Unbound |
Affected:
0 , < 1.26.1
(semver)
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Date Public
2026-09-16 00:00
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CVE-2026-80225 (GCVE-0-2026-80225)
Vulnerability from cvelistv5 – Published: 2026-09-16 08:30 – Updated: 2026-09-16 14:33
VLAI
EPSS
VEX
Title
Possible degradation of service from continuous queries on the same TCP/DoT connection
Summary
In NLnetLabs Unbound up to and including 1.26.0, a degradation of service vulnerability is present in the TCP/DoT reading procedure where there is no limit on consecutive reads. A malicious actor that can stream and sustain a rate of distinct uncached names over the TCP/DoT connection, monopolizes a single worker's entire event loop for as long as its writes stay ahead of the drain.
Severity
5.3 (Medium)
SSVC
Exploitation: none
Automatable: yes
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-16 14:32 UTC
CWE
- CWE-770 - Allocation of Resources Without Limits or Throttling
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
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Affected:
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Date Public
2026-09-16 00:00
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CVE-2026-78227 (GCVE-0-2026-78227)
Vulnerability from cvelistv5 – Published: 2026-09-16 08:29 – Updated: 2026-09-16 15:33
VLAI
EPSS
VEX
Title
Use-after-free in DoQ stream output buffer on reset re-transmission
Summary
NLnet Labs Unbound 1.22.0 up to and including 1.26.1, has a use-after-free vulnerability when compiled for DNS-over-QUIC support with '--with-libngtcp2'. Each DoQ stream owns an output buffer that holds the DNS response. ngtcp2's retransmission buffer keeps a shallow pointer into the output buffer for as long as a STREAM frame may be resent. On a client RESET_STREAM, the output buffer is freed but ngtcp2 still holds the matching retransmission entries. The next PTO timeout makes ngtcp2 re-encode the STREAM frame and copy from the freed buffer. A malicious actor that can query Unbound over DoQ and that withholds ACKs, sends RESET_STREAM, and waits for PTO, reaches this use-after-free with no privilege. This leads to retransmissions against freed memory and eventually an abnormal server exit under a 20-query spray.
Severity
6.5 (Medium)
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-16 15:33 UTC
CWE
- CWE-416 - Use After Free
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | Unbound |
Affected:
1.22.0 , < 1.26.1
(semver)
|
Date Public
2026-09-16 00:00
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CVE-2026-77955 (GCVE-0-2026-77955)
Vulnerability from cvelistv5 – Published: 2026-09-16 08:29 – Updated: 2026-09-16 14:33
VLAI
EPSS
VEX
Title
Possible ZONEMD verification bypass window
Summary
In NLnet Labs Unbound 1.13.2 up to and including 1.26.1, a vulnerability in ZONEMD configured zones (zonemd-check: yes) which are located below (but not at) a trust anchor allow for an attack window where (tampered with) zone contents are served (or stored to disk) prior to the ZONEMD integrity check. This is caused by the needed DS/DNSKEY asynchronous resolution that needs to happen before the ZONEMD check completes. If a zonefile is written to disk (zonefile: option) while the ZONEMD check failed, the tampered data are reloaded on startup and available until ZONEMD verification concludes again. If verification fails, the data is not served any more but still persists on disk for future reloads.
Severity
4.4 (Medium)
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-16 14:33 UTC
CWE
- CWE-345 - Insufficient Verification of Data Authenticity
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | Unbound |
Affected:
1.13.2 , < 1.26.1
(semver)
|
Date Public
2026-09-16 00:00
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CVE-2026-77860 (GCVE-0-2026-77860)
Vulnerability from cvelistv5 – Published: 2026-09-16 08:29 – Updated: 2026-09-16 14:45
VLAI
EPSS
VEX
Title
'serve-expired' can bypass Unbound 'wait-limit'
Summary
In NLnetLabs Unbound 1.20.0 up to and including 1.26.0, a vulnerability on the 'serve-expired' code path can cause a double decrement on the 'wait-limit' counter per client IP essentially bypassing one of the counter measures that was introduced for DNSBomb (CVE-2024-33655). A malicious actor can exploit this by controlling an authoritative zone with short TTL, so cached entries expire quickly. Each 'slow' query, one the attacker's authoritative never answers, is followed by one query for an expired cached name, which is answered immediately via the 'serve-expired' path and decrements the counter twice. This second query was named 'pump'. By alternating slow queries and pumps, the attacker keeps the per-client counter at or below the configured 'wait-limit' indefinitely, and can hold an arbitrary number of pending queries from a single source IP, up to the global mesh quota (num-queries-per-thread); eventually bypassing one of the counter measures introduced for DNSBomb (CVE-2024-33655). This vulnerability is present on the 'serve-expired' code path.
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-16 14:45 UTC
CWE
- CWE-675 - Multiple Operations on Resource in Single-Operation Context
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | Unbound |
Affected:
1.20.0 , < 1.26.1
(semver)
|
Date Public
2026-09-16 00:00
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CVE-2026-19538 (GCVE-0-2026-19538)
Vulnerability from cvelistv5 – Published: 2026-08-26 08:47 – Updated: 2026-08-26 14:00
VLAI
EPSS
VEX
Title
Bypass of BLOCKED ACL items on proxy protocol port over TCP or TLS
Summary
The BLOCKED access control list items that are evaluated to deny access on the the proxy protocol port can be bypassed completely when connecting over TCP or TLS and sending the query twice on connection that is kept open.
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-08-26 13:51 UTC
CWE
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-1… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | NSD |
Affected:
4.8.0 , < 4.15.1
(semver)
|
Date Public
2026-08-26 12:00
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CVE-2026-19401 (GCVE-0-2026-19401)
Vulnerability from cvelistv5 – Published: 2026-08-26 08:44 – Updated: 2026-08-26 14:16
VLAI
EPSS
VEX
Title
Remote UDP DoS by sending multiple DNS Cookie options
Summary
Any remote client can crash a (debugging/non-release build type) NSD serve child by sending it a special crafted message with a specially tuned number of DNS Cookie options (17 when UDP payload size is 512). By continuously crashing the serve childs, the remote client can severely hamper or, when positioned sufficiently close, deny all DNS service.
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-08-26 14:09 UTC
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-1… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | NSD |
Affected:
4.3.7 , < 4.15.1
(semver)
|
Date Public
2026-08-26 12:00
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CVE-2026-18916 (GCVE-0-2026-18916)
Vulnerability from cvelistv5 – Published: 2026-08-26 08:39 – Updated: 2026-08-26 14:22
VLAI
EPSS
VEX
Title
Remote TCP DoS by throttling the TCP receive window
Summary
Any remote client can crash a NSD serve child, by throttling the TCP receive window after a TCP query. By continuously crashing the serve childs, the remote client can denial all TCP service to this NSD instance.
Severity
SSVC
Exploitation: none
Automatable: yes
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-08-26 14:17 UTC
CWE
- CWE-191 - Integer Underflow
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-1… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | NSD |
Affected:
3.2.11 , < 4.15.1
(semver)
|
Date Public
2026-08-26 12:00
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CVE-2026-18664 (GCVE-0-2026-18664)
Vulnerability from cvelistv5 – Published: 2026-08-26 08:34 – Updated: 2026-08-26 14:47
VLAI
EPSS
VEX
Title
Wrong interpretation of ACL ranges
Summary
When ranges are used for access control (i.e. of the form 1.2.3.4-1.2.3.25), because NSD wrongly compares the IP address with the range on little endian systems, IPs that were meant to be allowed may be denied, and, IPs that were meant to be denied access could be allowed. An IPv4 address is compared with IPv4 ranges as unsigned 32 bit numbers directly with the endianness of the host, but the values to compare are in network byte order (big-endian). With IPv6 addresses the comparison is done in 4 times a unsigned 32 bit number comparison, again with the endianness of the host where all values are actually in network bye order.
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-08-26 14:33 UTC
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-1… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | NSD |
Affected:
3.0.0 , < 4.15.1
(semver)
|
Date Public
2026-08-26 12:00
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CVE-2026-56444 (GCVE-0-2026-56444)
Vulnerability from cvelistv5 – Published: 2026-07-22 13:10 – Updated: 2026-07-22 13:58
VLAI
EPSS
VEX
Title
Degradation of resolution service when 'discard-timeout' and 'serve-expired-client-timeout' are combined in unusual configuration
Summary
In NLnet Labs Unbound 1.20.0 up to and including 1.25.1, when Unbound is configured with 'serve-expired: yes' and 'serve-expired-client-timeout > discard-timeout > 0' (contrary to the suggested values), the discard-timeout branch during the serve expired logic drops an aged client reply without performing the correct accounting for the number of reply addresses for the query. Other identical branches outside of serve expired perform the correct decrement. Since the counter is never decremented in such scenario, it can reach the maximum limit and new clients for duplicate in-flight queries are silently dropped resulting in degradation of resolution service. A malicious actor can exploit the vulnerability by querying the resolver for a client-controlled slow-on-demand authoritative zone that can drive the counter past the threshold. Shipped defaults for 'serve-expired-client-timeout: 1800' and 'discard-timeout: 1900' make the branch unreachable.
Severity
5.9 (Medium)
SSVC
Exploitation: none
Automatable: yes
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-07-22 13:58 UTC
CWE
- CWE-772 - Missing Release of Resource after Effective Lifetime
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
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Affected:
1.20.0 , < 1.25.2
(semver)
|
Date Public
2026-07-22 00:00
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CVE-2026-56416 (GCVE-0-2026-56416)
Vulnerability from cvelistv5 – Published: 2026-07-22 13:10 – Updated: 2026-07-22 14:00
VLAI
EPSS
VEX
Title
Possible heap buffer overflow when validator canonicalizes RDATA that contains domain name
Summary
In NLnet Labs Unbound up to and including version 1.25.1, when the validator builds the canonical RDATA form for an RRSIG-covered PX/RP/MINFO/SOA RRset, it computes the address of the second embedded domain name as 'datstart + dname_valid(datstart, ...)' and passes it straight to 'query_dname_tolower()' without checking that a second name is actually present in the RDATA. The wire-format parser accepts multi-dname RRs whose RDATA ends after the first name, so an attacker who runs a DNSSEC-signed authoritative server can deliver a record with an absent second domain name (e.g. SOA record) and cause 'query_dname_tolower()' to walk label-by-label through stale bytes in the per-worker 'env->scratch_buffer', past the end of that heap allocation if 'msg-buffer-size' has been lowered from the default. This leads to heap buffer overflow and on a release build the outcome relies heavily on the contents of the buffer tail and the adjacent heap chunk.
Severity
4.8 (Medium)
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-07-22 13:59 UTC
CWE
- CWE-354 - Improper Validation of Integrity Check Value
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | Unbound |
Affected:
0 , < 1.25.2
(semver)
|
Date Public
2026-07-22 00:00
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CVE-2026-55991 (GCVE-0-2026-55991)
Vulnerability from cvelistv5 – Published: 2026-07-22 13:10 – Updated: 2026-09-16 14:24
VLAI
EPSS
VEX
Title
Remote DNS-over-QUIC (DoQ) flow-control assertion failure in libngtcp2
Summary
In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, a remote unauthenticated client can trigger a libngtcp2 assertion (if compiled with assertions on) and terminate the entire Unbound process using a single DNS-over-QUIC (DoQ) connection and one normal DNS query. This is caused by an erroneous error value passed to libngtcp2. When 'ngtcp2_conn_writev_stream()' returns 'NGTCP2_ERR_STREAM_DATA_BLOCKED', Unbound continues to call 'ngtcp2_ccerr_set_application_error()' with a '-1' error value. The 'int' literal '-1' is implicitly converted to the function's 'uint64_t error_code' parameter as '0xFFFFFFFFFFFFFFFF'. The follow-on 'ngtcp2_conn_write_connection_close()' serialises that value as a QUIC variable-length integer; because '2^64-1' exceeds the 62-bit varint ceiling, 'ngtcp2_put_uvarintlen()' fails 'assert(n < 4611686018427387904ULL)' and the whole resolver process aborts. A remote, unauthenticated DoQ client can trigger this deterministically with a single QUIC connection by advertising 'initial_max_stream_data_bidi_local = 1' in its transport parameters and sending one DoQ query without ever reading the stream.
Severity
5.9 (Medium)
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-07-22 14:01 UTC
CWE
- CWE-195 - Signed to Unsigned Conversion Error
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | Unbound |
Affected:
1.22.0 , < 1.25.2
(semver)
|
Date Public
2026-07-22 00:00
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CVE-2026-55990 (GCVE-0-2026-55990)
Vulnerability from cvelistv5 – Published: 2026-07-22 13:10 – Updated: 2026-07-22 14:04
VLAI
EPSS
VEX
Title
Packet of death for a DNSCrypt misconfigured Unbound
Summary
In NLnet Labs Unbound 1.7.0 up to and including 1.25.1, when the 'dnscrypt:' clause lists more 'dnscrypt-provider-cert:' files than there are matching 'dnscrypt-secret-key:' files, Unbound fills only the matched prefix and leaves the tail slots at the '0xdb' fill that libsodium's allocator writes into every allocation. Unbound would then iterate over the number of cert files, not the actual slots, so it walks into a slot with garbage data filled with '0xdb' bytes. Any unauthenticated client that sends one UDP datagram of ≥ 68 bytes whose first 8 bytes are '0xdb' to 'dnscrypt-port' will use that garbage entry which leads to a garbage dereference killing the server. This is a silent faulty configuration that goes unnoticed until triggered with the right client query. Unbound needs to be compiled with DNSCrypt support ('--enable-dnscrypt').
Severity
5.9 (Medium)
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-07-22 14:04 UTC
CWE
- CWE-457 - Use of Uninitialized Variable
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | Unbound |
Affected:
1.7.0 , < 1.25.2
(semver)
|
Date Public
2026-07-22 00:00
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CVE-2026-55973 (GCVE-0-2026-55973)
Vulnerability from cvelistv5 – Published: 2026-07-22 13:09 – Updated: 2026-07-22 14:06
VLAI
EPSS
VEX
Title
'dns-error-reporting: yes' leads to stack buffer overflow
Summary
In NLnet Labs Unbound 1.23.0 up to and including 1.25.1, when 'dns-error-reporting: yes' is set, the EDNS Report-Channel option (code 18) from the last upstream response is read and uses the option's length as the length of the agent domain. When a domain name check is performed on the agent domain, the returned lenght is not used and if the agent domain is followed by garbage, those bytes are moved onto the tail of the synthetic '_er.' report query name. That query name is later used in the iterator via a subquery to send out the DNS Error Report and when Unbound tries to walk that query name during 'find_closest_of_type()', it strips labels using the query name length rather than stopping at the embedded root, walks one byte past it, and feeds the first garbage byte to 'dname_query_hash()' as a label length writing over the stack variable 'labuf'. One ordinary upstream response from a delegated zone the attacker controls is sufficient to terminate the daemon.
Severity
7.5 (High)
SSVC
Exploitation: none
Automatable: yes
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-07-22 14:05 UTC
CWE
- CWE-20 - Improper Input Validation
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | Unbound |
Affected:
1.23.0 , < 1.25.2
(semver)
|
Date Public
2026-07-22 00:00
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CVE-2026-55717 (GCVE-0-2026-55717)
Vulnerability from cvelistv5 – Published: 2026-07-22 13:09 – Updated: 2026-07-22 14:07
VLAI
EPSS
VEX
Title
'serve-expired-client-timeout' and 'response-ip' CNAME redirect could lead to a crash
Summary
In NLnet Labs Unbound 1.10.0 up to and including 1.25.1, when 'serve-expired: yes' is set together with a 'response-ip: <net> redirect' /'response-ip-data: <net> CNAME <target>' rule (or the RPZ 'rpz-cname-override' equivalent), a remote client who controls any delegated domain can crash the daemon. The serve-expired-client-timeout callback runs a two-pass loop to chase the respip-generated CNAME alias; on the second pass it resets 'alias_rrset' but not 'partial_rep'. Later, this inconsistency leads to a NULL pointer dereference and an eventual crash. A malicious actor can exploit the vulnerability by controlling any zone that replies with an A/AAAA record that falls inside the configured response-ip/rpz subnet. By delaying the answer when the previous record has expired, the vulnerable path of 'serve-expired-client-timeout' is taken leading to denial of service via the server crash.
Severity
5.9 (Medium)
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-07-22 14:07 UTC
CWE
- CWE-476 - NULL Pointer Dereference
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
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Affected:
1.10.0 , < 1.25.2
(semver)
|
Date Public
2026-07-22 00:00
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CVE-2026-55708 (GCVE-0-2026-55708)
Vulnerability from cvelistv5 – Published: 2026-07-22 13:09 – Updated: 2026-07-22 14:10
VLAI
EPSS
VEX
Title
Privacy/configuration issue when adding local data in views through 'unbound-control'
Summary
In NLnet Labs Unbound 1.6.0 up to and including 1.25.1, the 'view_local_data' and 'view_local_datas' commands of 'unbound-control' create a bare local zones tree for an already configured named view when the view is configured with no local data to begin with. However, the creation through the control interface omits adding the default-protected zones (e.g., RFC 1918 reverse, AS112 zones, .onion, .localhost). Once the local zone tree exists without the defaults, every query for a default-protected name from a client mapped to that view escapes to the public DNS via the iterator instead of being answered locally, bypassing local policy expectations.
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-07-22 14:09 UTC
CWE
- CWE-1188 - Initialization of a Resource with an Insecure Default
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| NLnet Labs | Unbound |
Affected:
1.6.0 , < 1.25.2
(semver)
|
Date Public
2026-07-22 00:00
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CVE-2026-54478 (GCVE-0-2026-54478)
Vulnerability from cvelistv5 – Published: 2026-07-22 13:09 – Updated: 2026-07-22 14:14
VLAI
EPSS
VEX
Title
DNS Cookie bypass when combined with proxy-protocol use
Summary
In NLnet Labs Unbound 1.18.0 up to and including 1.25.1, when Unbound listens on a 'proxy-protocol-port' interface with 'answer-cookie: yes', the RFC 9018 server-cookie SipHash is computed over the proxy's wire address instead of the PROXYv2-declared client. One server cookie obtained through a given proxy node therefore validates for every PROXYv2-declared source behind that node. On a UDP+proxy-protocol front, an off-path attacker can harvest one cookie with a single legitimate query, then replay it under any spoofed source and pass DNS Cookie checks that were deployed to defeat this in the first place.
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-07-22 14:14 UTC
CWE
- CWE-290 - Authentication Bypass by Spoofing
Assigner
NLnet Labs
CNA
References
1 reference
| URL | Tags |
|---|---|
| https://www.nlnetlabs.nl/downloads/unbound/CVE-20… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
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Affected:
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(semver)
|
Date Public
2026-07-22 00:00
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